The invention relates to a method and arrangement for marking a digitally encoded video and/or audio signal so as to classify said signal as authentic programme material. The invention also relates to an arrangement for decoding said marked signal and a recording medium on which said marked signal has been recorded.
Video and audio signals are increasingly transmitted and recorded in a digitally encoded form, for example, an MPEG bitstream. There is a growing need to accommodate a marker in said signal so as to classify the signal as authentic programme material. Marking digital signals is particularly useful in copy protection applications. The mark, also referred to as watermark, can effectively take the form of a single bit indicating that the signal constitutes copy protected material, or a multi bit code representing the originator of the material. Watermarking is comparable to placing an electronic stamp on the video and audio material.
In the known MPEG standard for audio and video compression a copy protection bit has been defined for that purpose. However, a disadvantage of this known method is that the protection bit can easily be detected and then modified so as to circumvent a copyright protection mechanism.